While one of the functions of circulating drilling fluid during the drilling of a well is to prevent drill cuttings from accumulating in the borehole by carrying them to the surface, such circulation may not completely remove all such cuttings (and other debris) from the borehole. Moreover, the conventional circulation of drilling fluid during drilling is particularly inefficient for cleaning out drill cuttings in many high-angle and horizontal wells, sometimes resulting in the formation of a layer of drill cuttings and other solids settling along the low side of the high angle and horizontal drill sections; this is sometimes known as a cuttings bed. The formation of a cuttings bed can cause additional difficulties, for example, by causing increased torque and drag on the drill string.